The term “food effect” refers to a somewhat unpredictable phenomenon that can influence the absorption of drugs from the gastrointestinal tract following oral administration. A food effect can be designated “negative” when absorption is decreased, or “positive” when absorption is increased and manifested as an increase in oral bioavailability (as reflected by total exposure, usually defined as AUC). Alternatively, food effects can refer to changes in maximum concentration (Cmax), or the time to reach maximum concentration (Tmax), independently of overall absorption. As a result, some drugs have to be taken in either fasted or fed conditions to achieve the optimum effect. For example, patients may be instructed to take a drug with a meal, before a meal (e.g., one hour before a meal), or after a meal (e.g., two hours after a meal). However, many drugs are unaffected by food, and thus, can be taken in either a fasted or a fed condition.
Doxepin is a tricyclic compound currently approved for treatment of depression and anxiety. The recommended daily oral dose for the treatment of depression or anxiety ranges from 75 milligrams to 300 milligrams. Also, U.S. Pat. Nos. 5,502,047 and 6,211,229 describe the use of doxepin for the treatment chronic and non-chronic (e.g., transient/short term) insomnia. Doxepin, unlike most FDA-approved products for the treatment of insomnia, is not a Schedule IV controlled substance. Historically, doxepin pharmacokinetics have not been known to be affected by food.
In treating depression, anxiety and sleep disorders it is beneficial to optimize the pharmacokinetics of the administered medication in a patient. For example, in the case of sleep disorders a patient may have a set window of time within which they desire that their sleep occur. Thus, it can be useful to minimize the amount of time required to attain a maximum concentration of a drug in order to receive the therapeutic benefit of the drug as soon as possible during the desired treatment period.